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Unread 06-18-2004, 06:59 AM   #1
statjunk
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Bathroom Tile Question

A friend of mine just contracted a guy to gut his entire bathroom. I was checking out the guys work and was wondering if it is ok.

Here is what I saw: The floor joists are 2x8's 16 oc. There are the typical cross planks, I would say about 3/4" think with spaces in between them. Then there is about 3/8" plywood on top of that. Then there is a fairly thick layer of thinset, approx 1/4" thick, then 1/2" cement board. I noticed the the seams on the cement board weren't taped and mudded.

What are you thoughts on this?

Thanks for the info

Tom
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Unread 06-18-2004, 07:57 AM   #2
bbcamp
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Tom, it looks like a fair job, so far.

The plywood should be 1/2" thick (15/32 is what you'll probably find stamped on it). 3/8" is a little under sized, based on the Tile Council recommendations.

The thinset should be combed with a 1/4" square notch trowel, or as specifed by the backerboard manufacturer. It will squish down to fill any voids between the backer and the plywood. If it wasn't combed out, the backerboard will probably be lumpy unless the setter did a great job keeping the thinset uniformly thick.

The seams between backerboard sheets must be taped and mudded, but that can be done as the tiles are set. Many pros do it this way so they won't create "speed bumps" at the seams.

Bob
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Unread 06-18-2004, 08:41 AM   #3
statjunk
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Bob,

Why must the seems be taped? Is it for moisture?

Also the unsupported span of the joists is about 12-14 ft.

TT
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Unread 06-18-2004, 09:50 AM   #4
bbcamp
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The seams are taped so the backerboards become a single unit. Backerboard systems are trying to emulate old-fashioned mud beds, which are monolithic structures.

You sure about the unsupported span of 12 to 14 feet? That's a waaaay over-span for 2x8s, and pushing 2x10s to the limit. Did you overlook a wall downstairs?
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Unread 06-18-2004, 11:06 AM   #5
statjunk
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Well I went with longest one. Two of the floor joists are about 9-10' long and then the rest are about 12-14' long. I didn't measure. I am eyeballing it.
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Unread 06-18-2004, 12:22 PM   #6
bbcamp
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How does the floor feel when you walk on it? Springy? Stiff?
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Unread 06-18-2004, 02:36 PM   #7
statjunk
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Bob,

Thanks for taking the time to look answer these questions.

Unfortunetly I haven't been able to walk on it since the marble tile the guy layed on it was drying at the time.

However even if the floor is screwed up I still saved my friends a$$ because it turns out that the "contractor" was going to use mastic to do the walls. I immediately told my friend to tell him no way. Use thinset.

Does the fact that he is using marble make things any different? I don't know the properties of marble. Does it need a stiffer floor or can it get buy with a little more give. The grout joints are 1/16"

Thanks
Tom

P.S. He is using white pre-mixed thinset in a bucket to do the marble.
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Unread 06-18-2004, 05:31 PM   #8
Jason_Butler
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For natural stone ( Marble, granite, travertine, limestone, etc) the floor must meet L/720 deflection specs. This is twice as stiff as the L/360 for ceramic.

As for the mastic, it's really not a big issue on walls since they don't see any load or moisture. If the tiles are larger than 6" though i wouldn't go with mastic. It will never dry out and the grout will likely crack

Smaller tiles have more grout area and will allow better drying of the mastic.

Set the stone at 1/16" grout joint and get away from that MMMMMASTIC !.

That is not real thinset. There is no way you can mix a cementious product, stick it a bucket, store it on a shelf for months, and then use it to set floor tile. It may say thinset but it's not. Only the powder in the bag ( mix with water) is acceptable for floors

Those manufacturer's should be strung up for advertising as such

Jason
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